A torque converter is a type of hydrodynamic (fluid) drive used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load. A torque converter has at least three rotating elements: the pump or impeller, which is mechanically driven by the prime mover; the turbine, which drives the load; and the stator, which is interposed between the impeller and turbine so that it can alter drive fluid flow returning from the turbine to the impeller.
Currently, many automotive torque converters include a lock-up clutch to improve cruising power transmission efficiency. The application of the clutch locks the turbine to the impeller, causing all power transmission to be mechanical, thus eliminating losses associated with the fluid drive. These conventional torque converters, however, are both expensive and complicated. The lock-up clutches, in particular, require a separate hydraulic fluid circuit to move a slidable piston which has friction plates that allow the torque converter to lock up.
Additionally, these conventional systems often use a hollow turbine output shaft (i.e., the transmission input shaft) to supply the clutch's operating fluid. This hollow output shaft is an inherent weak point of these prior art automatic transmissions. This is particularly true in high torque and/or high RPM applications, such as racing.
Furthermore, if a user wishes to adapt a vehicle that ordinarily does not have a lock-up torque converter, conventional systems require the removal of the entire transmission or expensive modifications to the transmission.
Still further, in all torque converters, rotation generates centrifugal pressure within the torque converter housing (i.e., the impeller's outer shell and front cover) which results in expansion or “ballooning” of the housing. Ballooning is ordinarily a significant problem for conventional torque converters as this growth or expansion of the housing can result in catastrophic failure, such as bursting, under high RPMs or high torque. This ballooning also results in undesirable thrust imparted axially along the crankshaft.
Conventional torque converter designs seek to eliminate or reduce ballooning by using thicker and/or stronger housing materials and by providing additional bracing with so-called anti-ballooning plates which are externally mounted to the housing.
The present invention, takes advantage of torque converter ballooning in the elastic range by having this centrifugally enhanced internal pressure activate a lock-up clutch. The result is a torque converter that ultimately has reduced ballooning. The lock-up clutch is mated to an internal load piston which operates as an internal anti-ballooning plate; whereby the converter trades ballooning for lock-up capacity.
Some prior art references pertaining to lock-up type torque converters which rely on centrifugal forces to activate the clutch include U.S. Pat. No. 4,063,623 issued Dec. 20, 1977 to John Saxon Ivey et al. for “Fluid Coupling with Centrifugal and Torque Responsive Lock Up Clutch”; U.S. Pat. No. 3,465,328 issued Dec. 23, 1967 to John Bilton for “Fluid Coupling with Centrifugal Lock Up Clutch”; U.S. Pat. No. 3,252,352 issued May 24, 1966 to Norman T. General et al. for “Hydrokinetic Power Transmission Mechanism”; and U.S. Pat. No. 6,508,345 issued Jan. 21, 2003 to Tokuji Yoshimoto et al. for “Lock Up Clutch for Torque Converter”.
Generally such prior art cannot be readily adapted to vehicle transmissions that do not have a lock-up clutch. Further, these prior art systems do not disclose the novel use of torque converter ballooning to activate the lock-up clutch.